When President Bush asked Congress this week to consider whether the military should take the leading role in disaster response, he was merely picking up where other politicians have left off. Washington has long sought to induce the Pentagon to take a larger share of homeland security in times of crisis - from the war on drugs to the war on terror.

The notion has enraged civil libertarians and wary members of Congress, who fear the power of a military let loose on its own people. Yet in many respects, the greatest opponent of giving the military more authority at home has been the military itself.

It is a reluctance born of a martial ethos - the insistence that the military exists to fight the nation's wars, not to act as police. The fact that America remains at war in Iraq and Afghanistan has only deepened those reservations. So far, the Department of Defense has not taken a public stance on the president's idea, yet among many in the military community, there is concern that any major revision of the military's homeland mission could be both unnecessary and counterproductive.

"The military needs to focus on its core competencies - fighting wars," says Loren Thompson, a defense analyst at the Lexington Institute in Arlington, Va. "If we load the military with every mission that other cabinet agencies don't do well, then it won't be able to do its job well."

Indeed, Mr. Bush appears to be turning to the military in part because it was the only federal institution perceived to be competent in the aftermath of hurricane Katrina. Now, he and others are saying that the military might be the only federal asset able to respond quickly and effectively to disasters that overwhelm local police, fire, and emergency teams - as Katrina did. "Is there a natural disaster of a certain size that would then enable the Defense Department to become the lead agency in coordinating and leading the response effort?" Bush asked at a briefing last weekend.

What this might mean for the military, however, is a task that the president has left to Congress. Sen. John Warner (R) of Virginia, chair of the Armed Services Committee, has said that Congress needs to consider amending Posse Comitatus - the Reconstruction-era law that prohibits federal troops from taking part in law-enforcement operations.

The law does not affect National Guard troops, because they are called up by their governors and therefore under local control. But with so many Guard soldiers in Iraq, and with the scope of the damage in the Gulf Coast region, other lawmakers agree that Congress must consider expanding the authority of active-duty forces after a catastrophic disaster.

"[Katrina] does represent a significant change, and I think we'll have to explore carefully whether the only option we have to increase the effectiveness of response ... is to break the normal line that keeps the military out of certain civilian activities," Sen. Susan Collins, chair of the Homeland Security Committee, said at a Monitor breakfast this week.

It is a move that military leaders have resisted in the past. The issue is not so much Posse Comitatus itself, which legal experts say has many loopholes, but what Posse Comitatus represents. It is part of a doctrine that sees the American military primarily as a war-fighting force. It shields the armed forces from the burden of additional domestic duties - and the possibility of being involved in an incident like Kent State, where National Guard soldiers killed four antiwar protesters in 1970.

After the Sept. 11 attacks, Gen. Thomas White told Congress that Posse Comitatus "is fine the way it sits."

Today, any move to amend Posse Comitatus, say military analysts, would represent not only a move in the wrong direction, but also a misapprehension of the situation.

For one, it is unnecessary, they say. The active-duty military can already support disaster relief in a variety of ways that are in accord with Posse Comitatus - providing logistics and humanitarian aid, for example, as has happened in the Gulf Coast region. For law enforcement, emergency officials have the National Guard - and if one state's Guard is depleted by overseas deployments, it can ask for help from other states through their network of Emergency Management Assistance Compacts.

Defense Secretary Donald Rumsfeld suggested as much in a Pentagon briefing this week, noting that some 300,000 Guard members were available across the country even at the peak of the Katrina deployment. "And of course the Guard, as opposed to the active force, tends to have a higher proportion of people who do things that are appropriate in a domestic setting," he added.

Moreover, if a disaster is deemed too great even for the National Guard, the president has the authority to federalize the response, which would bring in active-duty troops as law enforcement - something that occurred in 1992 during the Rodney King riots in Los Angeles.

But federalizing disaster response can be a tricky prospect, fraught with tensions between Washington and state officials. Those tensions were apparent Tuesday, when Michael Brown, former Federal Emergency Management Agency director, blamed local officials for the ineffectual response to Katrina.

With no concrete plans in place, Secretary Rumsfeld said Tuesday that it is too early to pass judgment on the president's comments. But some observers wonder whether the current push to increase military involvement is simply a way for the administration to avoid the tough choices.

The military can help with logistics and planning and response, but "the important decisions that need to be made are political," says retired Col. Randall Larsen, founder of the Institute for Homeland Security. "It's not a four-star general who should be making them."